<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>test2</title>
  </head>

  <body>
    <script src="./js/observer.js"></script>
    <script>
      var people = {
        age: 18
      }
      observer(people)
      people.age = 20
    </script>
  </body>
</html>
